Device-to-device (D2D) communication or vehicle to vehicle (V2V) communication is a technology in which communications nodes directly communicate with each other. The communications nodes directly communicate with each other by using a radio resource allocated by a base station.
A communications node is usually synchronized with a base station to which the communications node belongs. When a plurality of communications nodes separately belong to different base stations, if the base stations are not synchronized with each other, the plurality of communications nodes that separately belong to the different base stations are not synchronized with each other either. Therefore, when the plurality of communications nodes that separately belong to the different base stations perform D2D communication or V2V communication with each other, the communications nodes cannot transmit data to each other because the communications nodes are not synchronized with each other. For example, a communications node 1 accesses a base station 1, and a communications node 2 accesses a base station 2. If the base station 1 is not synchronized with the base station 2, the communications node 1 is not synchronized with the communications node 2 either. When the communications node 1 performs D2D communication or V2V communication with the communications node 2, for example, in the V2V communication, if a sudden accident occurs on a vehicle in front, it is required that information indicating that an accident occurs on the vehicle in front can be received by another vehicle in time. For example, the vehicle in front serves as the communications node 1, and the another vehicle serves as the communications node 2. The communications node 1 sends a data subframe at a moment 1. Because the communications node 2 is not synchronized with the communications node 1, the data subframe has not arrived at a moment 1 of the communications node 2. Therefore, the communications node 2 cannot correctly receive the data subframe sent by the communications node 1. This severely affects reliability and safety for the D2D communication, especially, in the V2V communication.
Therefore, a technical solution is urgently required in the industry to improve reliability and safety for the D2D communication and the V2V communication.